This invention relates to imaging systems and in particular to a novel migration imaging system utilizing electrophotographic techniques.
Migration imaging systems are described in U.S. Pat. No. 3,520,681 to William L. Goffe and in copending applications Ser. Nos. 837,591 and 837,780 both filed June 30, 1969. In migration imaging migration material imagewise migrates in depth in a softenable material. In a typical embodiment an electrical latent image is created on an imaging member composed of marking particles dispersed in, or layered in, or layered on, a softenable material. Development of this latent image is effected by reducing the resistance of the softenable material to marking particle migration, i.e., it is rendered permeable to the marking particles. Certain marking particles migrate because they associate with the charge of the latent image and the migrated and non-migrated particles constitute complementary images. The complimentary images may be separated by various techniques, e.g., the softenable material may be dissolved and washed away, freeing the migrated image but at the expense of losing the non-migrated image. Alternately, the softenable material may be split at a level between migrated and unmigrated particles, thereby freeing both images, as described in copending application U.S. Ser. No. 784,164, filed Dec. 16, 1968 now U.S. Pat. 3,741,757.
Several different embodiments of the process are possible by varying the composition of the materials, charging levels, light intensities and other parameters of the process. One embodiment employs photosensitive particles, e.g. selenium, embedded in a layer at or near the surface of a softenable material. This member is uniformly charged and exposed to light in imagewise configuration creating an electrical latent image. This latent image need not be characterized by distinct differences in charge density between exposed and unexposed areas as in xerography. The essential mechanism is believed to be that the charge in the exposed areas is capable of becoming associated with adjacent selenium particles at least when the permeability of the softenable material is increased. In this embodiment, typically the selenium particles exposed to light migrate in depth in the softenable material forming a negative image of the original while the non-migrated particles form a complementary positive image. (The terms "positive and negative" images are used in the classical photographic sense with a positive image having areas of light and dark tones corresponding to areas of light and dark tones in an original with the negative image being the inverse of the positive image.)
Another migration imaging embodiment employs an imaging member composed of photosensitive particles randomly dispersed throughout the bulk of a softenable material matrix. This member is uniformly charged and exposed to light in imagewise configuration to create an electrical latent image. Here, the photosensitive particles and/or matrix are capable of dissipating charge from the surface of the member to a conductive substrate in the areas exposed to light. Here the resultant latent image is usually characterized by differences in charge density in exposed and non-exposed areas. The particles adjacent the charged areas associate with the charge and migrate toward the substrate when the permeability of the matrix is increased.
Yet another migration imaging embodiment employs an imaging member having non-photosensitive marking particles on or in a non-photosensitive softenable material matrix. The electrical latent image is created by selectively charging areas of the member as through a stencil or by other charge pattern generating or transferring techniques. The marking particles adjacent the charge become associated with the charge and migrate toward a substrate to form an image.
The permeability of the softenable matrix is increased by methods that include exposing it to heat, solvent vapors, solvent liquids and combinations thereof.
Surface deformation imaging systems are described in a paper by R. W. Gundlach and C. J. Claus titled "A Cyclic Xerographic Method Based on Frost Deformation" in Photographic Sciences and Engineering, Vol. 7, No. 3, pp. 14-19, January - February 1963. Additional descriptions are given in U.S. Pat. Nos. 3,196,011 to K. W. Gunther and R. W. Gundlach and 3,113,179 to W. E. Glenn, Jr. Two distinct surface deformation imaging systems have evolved: relief imaging and frost imaging. Both imaging systems employ a softenable film (hereafter called a deformable material) overcoating a conductive substrate. Surface deformations occur in both relief and frost systems due to electrical forces exerted on the deformable material when its viscosity is reduced. The deformations in relief imaging are highly regular in shape because they are caused by forces lateral to the surface associated with abrupt changes in charge density. The deformations in frost imaging include randomly shaped depressions generally uniformly spaced over an area of the frostable material having constant or continuously charging charge densities above threshold levels for frosting. The threshold level for frosting is presently believed related to such parameters on ion mobility, viscosity, bulk conductivity, surface conductivity and thickness of the frostable material. During the frost deforming process, the frostable material circulates or flows in a manner similar to convection currents. Circulating action including frost circulation is employed in the present invention to form novel migration imaging processes and imaged members.
U.S. Pat. No. 3,542,545 discloses the frost or relief wrinkling of an electrically photosensitive layer overlying a deformable layer. The electrically photosensitive layer comprises two configurations: (1) a fracturable film of particles which may be disrupted and relocated into valleys or wrinkles on the surface of the deformable layer in its deformed state, and (2) a layer of binder material and particles which does not fracture nor relocate into valleys but which deforms in the same configuration as the underlying deformable layer in its deformed state. However, in both configurations, the particles do not penetrate the photosensitive layer - deformable layer interface, nor do they migrate into the deformable layer, migration is undisclosed.
Copending application Ser. No. 837,591, filed June 30, 1969 which is a continuation-in-part of Ser. No. 634,757 filed Apr. 28, 1967, discloses a migration imaging member comprising a softenable layer having marking material dispersed therein overlying an additional second softenable layer residing on a suitable imaging substrate. This member may be imaged so that the particles migrate from the top softenable layer straight down into the second softenable layer. This member has proven useful for removing background particles retained in the top layer from the imaged particles, migrated into the second layer so as to enhance image clarity, by simply splitting the top and second softenable layers. However, in use, it is preferred that this migration imaging member have materials in the softenable layers similar to one another, such as miscible materials, so that virtually no effective interface exists between the layers to impede, retard or prevent the migration of particles therebeyond. Additionally, by migrating straight into the second softenable layer, the migrating particles do not group and therefore there is no transparentizing or window opening effect.